This invention relates to a method of detecting a defect in an object such as a bottle, and an apparatus for implementing the method.
If a bottle made of glass for wine, alcoholic liquors, soft drinks or foods has a defect such as scratches, cracks or breakages at its mouth, then it is impossible or difficult to completely seal the mouth, and problems in food hygiene occur. Thus, it is necessary to detect a defect and to reject the bottles having a defect. It is also necessary to detect a defect at other parts, such as the bottom of a bottle for maintaining food hygiene.
A variety of methods of detecting defects in bottles have been proposed in the art; however, they still have the following difficulties:
For instance, in a defect detecting apparatus disclosed in Japanese Patent Application Laid-Open No. 108881/1976, a bottle conveyed by a conveyor is stopped at an inspection station, where it is spinned at a high speed, and it is inspected by a pair or plurality of light emitting and light receiving units which are arranged around the mouth of the bottle. However, the apparatus is disadvantageous in that it is intricate in mechanical construction, and its inspection speed is low, e.g., at about one hundred bottles per minute.
Japanese Patent Application Publication No. 43218/1974 and Japanese Patent Application Laid-Open No. 17779/1978 discloses a method in which, while a bottle is passed through an inspection position, light is applied to the mouth portion of the bottle, and light reflected from all the surface of the mouth portion is detected by rotating a prism and a reticle at a high speed, whereby a defect is detected. In this method, it is unnecessary to spin a bottle at a high speed; however, it is necessary to provide a high-speed rotation mechanism for spinning the prism or reticle at a high speed. Accordingly, it is difficult to maintain the accuracy high for a long period of time, and it also difficult to increase the rate of inspection.
Also known in the art is a method in which light reflected from a bottle's mouth portion is detected with a number of light emitting and light receiving units. However, the method has a drawback in that the entire mouth portion cannot be inspected uniformly.